Carbonylation Reactions of a Metallapentalyne: Synthesis of Its Ester and Amide Derivatives

Abstract

Carbonylation reactions are a valuable synthetic method to construct carbonyl compounds and carbonylation reactions of aryl halides stand out as a highly significant tool for generating carbonyl substituted arenes. However, the important reactions have never been realized in aromatic metallacycles. Herein, we present the first carbonylation reactions of metallaaromatics, specifically alkoxycarbonylation and aminocarbonylation reactions of an osmapentalyne. During the carbonylation process, the electronic and steric properties of nucleophiles are regarded as critical factors. The alcohols with bulky substituents (isopropanol) require more reaction time and tert-butyl alcohol is inert in the reaction. Comparatively, amines, being stronger nucleophiles, exhibit divergent behaviors. Bulky amines undergo aminocarbonylation, whereas small amines prefer direct nucleophilic additions. Control experiments revealed that the intermediate derived from coupling of metal carbyne with CO plays a significant role in the carbonylation reaction. According to these observations, a divergent pathway for the reaction is proposed. Furthermore, the photophysical properties of these carbonyl-functionalized osmapentalene complexes are studied, and the maximum absorption peak of compound with a carboxylic group exhibits a significant red-shift due to the smaller HOMO-LUMO gap. These findings contribute to expanding the reactivity of metallaaromatics and offer new opportunities for the synthesis of carbonyl-functionalized metallacycles.

Keywords

Carbonylation reactions / Metal carbyne / Aromaticity / Carbon monoxide / Metallacycle

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